In recent years, developments of vectors for delivering drugs, nucleic acids, peptides, proteins, sugars and the like certainly to target sites have been actively carried out. For example, for gene therapy, viral vectors such as retrovirus, adenovirus, adeno-associated virus and the like have been developed as vectors for introducing a desired gene to a target cell. However, since the viral vectors have problems such as difficulties in mass production, antigenicity, toxicity and the like, liposome vectors, which suffer less from such problems, have attracted attention. The liposome vectors have an advantage that the directivity to a target site can be enhanced by introducing functional molecules such as antibodies, proteins, sugar chains and the like to the surface of the liposome vectors.
As a method for preparing liposomes, for example, there is known a lipid film hydration method. According to the lipid film hydration method, multilamellar liposomes encapsulating an object material can be prepared by hydrating a lipid membrane in the presence of the object material such as genes (see Non-Patent Document 1). New lipid membranes can be further laminated on the external side of the multilamellar liposomes by repeatedly applying the lipid film hydration method to the multilamellar liposomes thus prepared. As such, by repeating the lipid film hydration method, the number of the lipid membranes included in the multilamellar liposomes can be increased.    [Non-Patent Document 1] Kogure, et al., Journal of Controlled Release, Vol. 98, pp. 317-323 (2004)